Various semantic changes in email text, footer, and event page

[grablair]

This is a minor change that modifies some text in emails and in the title of event pages.

1. It ensures all emails end with the app name, and normalizes the format of that section of the email
2. Changes the default email footer to "© <year> <app-name> | Powered by Hi.Events" with Hi.Events linked to https://hi.events?utm_source=app-email-footer. My thinking is that the actual content of the email may not be copyrighted to Hi.Events; and it changes the footer to the "Powered by" verbiage, as that's what is in the LICENCE, so it makes it consistent with the license and elsewhere in the code.
3. Changes the event page title to end with the organizer name instead of "Hi.Events" (i.e. "My Great Event | Cool Theater"). My thinking is that users should clearly know who is organizing the event.

Very open to thoughts on points 2 and 3.

Checklist

• I have read the contributing guidelines.
• My code is of good quality and follows the coding standards of the project.
• I have tested my changes, and they work as expected.

Thank you for your contribution! 🎉

[daveearley]

These changes all make sense to me. Thanks for the PR!